"Eien" is a Japanese word that means "eternity" or "forever." Some synonyms that can be used to convey similar meanings are "forevermore," "perpetual," "enduring," "tenacious," "unfaltering," and "unceasing." These words all represent something that lasts a long time or is unchanging. In a spiritual context, synonyms for "eien" might include "divine," "sacred," "holy," or "eternal." All of these words evoke a sense of permanence that is unbreakable, indestructible, and infinite, and they can be used interchangeably with "eien" depending on the context and the tone of the writing.